CN114644369A

CN114644369A - Preparation method and application of LNMC622@ LRNMC composite material

Info

Publication number: CN114644369A
Application number: CN202210075521.8A
Authority: CN
Inventors: 王舜; 金辉乐; 陶琪琪; 陈锡安; 李俊; 张礼杰
Original assignee: Institute of New Materials and Industrial Technology of Wenzhou University
Current assignee: Institute of New Materials and Industrial Technology of Wenzhou University
Priority date: 2022-01-22
Filing date: 2022-01-22
Publication date: 2022-06-21
Anticipated expiration: 2042-01-22
Also published as: CN114644369B

Abstract

The invention discloses a preparation method of an LNMC622@ LRNMC composite material, which comprises the following steps: s1: mixing zirconium oxide ball milling beads, LRNMC and anhydrous n-hexane solution, ball milling, and drying to obtain LRNMC particles; s2: mixing and grinding an NMC622 precursor and anhydrous LiOH, calcining under an oxygen atmosphere, and cooling to obtain LNMC622 particles; s3: adding the LRNMC particles obtained in the step S1 into anhydrous n-hexane for ultrasonic dispersion, adding the product LNMC622 obtained in the step S2 after dispersion, stirring, drying and calcining to obtain the LNMC622@ LRNMC composite material. The preparation method is to modify the surface of a commercial LNMC622 material by a solid phase coating method to obtain the LNMC622@ LRNMC composite material which can be used as a battery anode material. The preparation method is simple, the cost is low, the electrochemical performance of the commercial ternary material can be obviously improved, and the ternary material can be used in the field of batteries and has good practical value and application prospect.

Description

Preparation method and application of LNMC622@ LRNMC composite material

Technical Field

The invention belongs to the technical field of inorganic functional materials and electrochemical energy, and particularly relates to a preparation method and application of LNMC622@ LRNMC.

Background

In order to alleviate the problem of energy shortage, the development of new clean energy storage systems is imminent. At present, the development of electric vehicles and hybrid vehicles has become one of the most promising strategies to solve the global fossil energy shortage problem. The lithium ion battery with high specific energy and high power is the key for realizing the large-scale commercialization of the electric automobile. Among them, nickel-rich layered structure oxides are one of the most desirable electrode materials due to their high energy density. However, the low cycle performance of conventional commercial nickel-rich materials limits their further applications.

The commercial material LNMC622 has a higher theoretical capacity due to its higher Ni content. At present, the industry has a mature process for producing the LNMC622 material. However, LNMC622 also has the disadvantages of nickel-rich materials, such as cation-mixing, easy generation of microcracks, and the like, thereby greatly limiting the application of the material. In response to the shortcomings of LNMC622, creating a nickel-rich material with a concentration gradient can improve the stability of the material while maintaining high capacity. The concentration gradient material is mainly characterized in that the surface of the material has high Mn content, and Mn plays a role in stabilizing the structure in the ternary material. However, concentration-gradient materials are often prepared by concentration-co-precipitation. The preparation method has no universality and is difficult to industrialize. In addition, inactive dopants generally do not contribute to effective capacity, and thus the doping content and species should be limited to a certain standard range. The modification process is relatively complex and difficult to industrialize, and needs to be further improved and simplified, so that more new materials and new engineering technologies are urgently needed to be researched to face the current problem of energy shortage. Therefore, it is a long-felt need to develop a nickel-rich electrode material with stable performance, safety and high energy density.

However, the lithium-rich manganese-based material is a material with low cost and good safety, and the Mn content of the material is high. Therefore, how to use the lithium-rich manganese-based material to perform surface coating on the commercial NMC622 material to prepare the gradient material is the key point for improving the performance and stability of the NMC622 material.

The invention content is as follows:

the present inventors have conducted intensive studies in order to solve the problems that the commercial nickel-rich material LNMC622 is susceptible to cation-shuffling, chemical-mechanical degradation, and phase evolution on the particle surface. The surface of the commercial LNMC622 material was modified by solid phase coating and a series of electrochemical performance tests were performed on the material. The present invention has been completed after a great deal of creative work has been done.

In order to realize the purpose of the invention, the specific technical scheme is as follows:

a preparation method of an LNMC622@ LRNMC composite material comprises the following steps:

s1: preparation of LRNMC microparticles:

s1.1: adding zirconium oxide ball milling beads with the diameter of 0.1-0.6 mm and an LRNMC material into an anhydrous n-hexane solution for ball milling, wherein the ball milling speed is set to be 300-600 rpm, and the ball milling time is set to be 20-60 hours;

s1.2: drying the material obtained in the step S1.1 for 5-8 hours at 50-70 ℃ in a vacuum drying oven, and sealing and storing for later use;

s2: preparation of LNMC622 material:

s2.1: the LNMC622 precursor was added to anhydrous LiOH, mixed and milled until no significant LiOH particles were present.

S2.2: and (2) under the condition of introducing high-purity oxygen, raising the temperature of the hydroxide obtained in the step (S2.1) to 400-600 ℃ at a temperature raising rate of 2-10 ℃/min, calcining at the temperature for 4-6h, continuing raising the temperature to 600-800 ℃ after 4-6h, calcining for 8-12 h, and reducing the temperature to obtain LNMC622 particles.

S2.3: and (3) grinding the LNMC622 particles obtained in the step (S2.2), sieving to obtain a material with uniform particles, and sealing and storing the material for later use.

S3: preparation of LNMC622@ LRNMC composite material

S3.1: and (4) adding the LRNMC material obtained in the step (S2) into a reagent bottle, adding an anhydrous n-hexane dispersing agent, and carrying out ultrasonic treatment on the reagent bottle after vacuum packaging for 2-4 hours to uniformly disperse the LRNMC material.

S3.2: and (3) adding the LNMC622 material into the ultrasonic dispersion liquid obtained in the step (S3.1), and placing the dispersion liquid on a stirrer to stir at 80-120 rpm for 10-14 h.

S3.3: and (4) putting the mixed material obtained in the step (S3.2) into a vacuum drying oven, drying for 1-4 h at 40-80 ℃, putting the dried material into a porcelain boat, and putting the porcelain boat into a tube furnace for calcination. The calcination conditions were: the heating rate is 2-10 ℃/min, and the temperature is increased to 600-900 ℃ for calcining for 1-4 h. And cooling to obtain the LNMC622@ LRNMC composite material.

According to the scheme, in the step S1.1, weighing 15-35 g of zirconia ball grinding beads with the diameter of 0.1-0.6 mm, weighing 1-5 g of LRNMC, and adding the LRNMC into 3-8 mL of anhydrous n-hexane;

according to the scheme, in the step S2.1, a certain amount of NMC622 precursor is weighed, and anhydrous LiOH with the amount of 0.5-1.5 times of that of NMC622 is weighed;

according to the scheme, in the step S3.1, 0.1-0.5 g of LRNMC material is added into a reagent bottle, and 3-8 mL of anhydrous n-hexane is added to serve as a dispersing agent;

according to the scheme, step S3.2 specifically includes adding 1-3 g of LNMC622 material into the ultrasonic dispersion liquid obtained in step S3.1.

The LNMC622@ LRNMC composite material prepared by the preparation method is applied to the field of electrochemical energy storage.

The invention has the beneficial effects that: in the LNMC622@ LRNMC composite material prepared by the method, the LNMC622 material is mixed by LRNMC, and a nickel-rich microsphere structure with gradually-changed element distribution is successfully constructed after high-temperature calcination, so that the cycle performance and the capacity retention rate of the LNMC622 material are greatly improved. After the LNMC622@ LRNMC composite cathode material is cycled for 200 times at 1C, the capacity retention rate is as high as 84%, and compared with the original NMC622 material, the capacity retention is improved by 24% in an integral manner, as shown in figure 7.

Drawings

FIG. 1 is a Scanning Electron Microscope (SEM) image of a 5% LNMC622@ LRNMC composite material prepared by the present invention.

FIG. 2 is a Transmission Electron Microscope (TEM) image of a 5% LNMC622@ LRNMC composite prepared according to the present invention.

FIG. 3 shows the powder X-ray diffraction patterns of LNMC622 and various coating amounts of LNMC622@ LRNMC composites prepared in examples 1-5 of this invention.

FIG. 4 is a Raman plot (Raman) of the LNMC622, LRNMC, 5% LNMC622@ LRNMC composite material made in example 1 of the present invention.

Fig. 5 is XPS high resolution spectra and XPS depth plots of Mn element and O element of LNMC622@ LRNMC composite.

Fig. 6 is a graph of the cycling performance under LNMC622 and 5% LNMC622@ LRNMC composite 1C.

Fig. 7 is a charge and discharge curve for LNMC622 and 5% LNMC622@ LRNMC composite 0.1C.

Fig. 8 is a graph of rate capability of LNMC622 and 5% LNMC622@ LRNMC composite.

Fig. 9 is a graph of cell impedance before and after cycling for LNMC622 and 5% LNMC622@ LRNMC composite.

Detailed Description

The present invention is described in detail below with reference to specific examples, but the use and purpose of these exemplary embodiments are merely to exemplify the present invention, and do not set forth any limitation on the actual scope of the present invention in any form, and the scope of the present invention is not limited thereto.

Example 1

S1: preparation of LRNMC microparticles:

s1.1: firstly, weighing 25g,0.3mm and 15g of zirconia ball milling beads with the diameter of 0.5mm and 2g of LRNMC material, adding the materials into 5 mL of anhydrous n-hexane solution for ball milling, and setting the rotation speed of the ball milling to be 500rpm and the time to be 48 h;

s1.2: drying the material obtained in the step S1.1 in a vacuum drying oven at 60 ℃ for 6h, and sealing and storing for later use;

s2: preparation of LNMC622 material:

S2.2: and (3) under the condition of introducing high-purity oxygen, raising the temperature of the hydroxide obtained in the step (S2.1) to 500 ℃ at the temperature raising rate of 5 ℃/min, calcining for 5h at the temperature, continuing to raise the temperature to 780 ℃ after 5h, calcining for 10h, and reducing the temperature to obtain LNMC622 particles.

S3: preparation of 5% LNMC622@ LRNMC composite material

S3.1: and (3) adding 0.1g of the LRNMC material obtained in the step (S2) into a reagent bottle, adding an anhydrous n-hexane dispersing agent, carrying out vacuum packaging on the reagent bottle, and carrying out ultrasonic treatment for 3 hours to uniformly disperse the LRNMC material.

S3.2: 1.9g of LNMC622 material was added to the sonicated dispersion obtained in step S3.1 and placed on a stirrer and stirred at 100rpm for 12 h.

S3.3: and (4) putting the mixed material obtained in the step (S3.2) into a vacuum drying oven, drying for 2 hours at the temperature of 60 ℃, putting the dried material into a porcelain boat, and putting the porcelain boat into a tube furnace for calcination. The calcination conditions were: the temperature rise rate is 5 ℃/min, and the temperature is raised to 750 ℃ for calcination for 2 h. After cooling, 5% of LNMC622@ LRNMC composite material is obtained.

Example 3-5 was performed by using step 2 described in example 1 as example 2, replacing the coating amount in step S3 of example 1 with 2%, 7%, 9%, and performing the same other operations, and the obtained materials were named LNMC622, 2% LNMC622@ LRNMC, 7% LNMC622@ LRNMC, and 9% LNMC622@ LRNMC, respectively.

Fig. 1 is a scanning electron microscope image of the 5% LNMC622@ LRNMC composite material prepared in example 1, and it can be seen from the image that the LRNMC has less scattering amount and more coating amount.

Fig. 2 is a transmission electron micrograph of the 5% LNMC622@ LRNMC composite prepared in example 1, wherein the lattice of the composite is clearly divided into two parts, the lattice fringe spacing inside the particles is 0.49nm, which is consistent with the lattice spacing of LNMC622, and a layer of thin different lattice fringes is distributed on the outermost layer of the particles, and is shown by white circles in fig. 2-b. This layer of lattice is then a lattice stripe of LRNMC. This shows that the LRNMC material has been successfully coated on LNMC622 particles by the above preparation process.

FIG. 3 is a powder X-ray diffraction pattern of the materials of examples 1-5 showing a shift in the diffraction peaks for the coated 5% LNMC622@ LRNMC as compared to LNMC 622. In this case, the larger the coating amount, the more significant the peak shift. This result is also easily understood, because the characteristic peak of LRNMC is different from the characteristic peak of LNMC622, and thus when the LNMC622 is coated with a layer of LRNMC material, the peak position is shifted.

Fig. 4 is a raman test chart of the LNMC622, LRNMC, 5% LNMC622@ LRNMC composite material prepared in the example of the present embodiment 1, and it can be seen that the 5% LNMC622@ LRNMC composite material not only has the characteristic peak of the LNMC622 and the characteristic peak of the LRNMC, and specifically, a part circled by a black circle in the figure. From raman tests, it can also be proved that the 5% LNMC622@ LRNMC composite material has the characteristics of both LNMC622 and LRNMC.

Fig. 5 is XPS high resolution spectra and XPS depth maps of Mn and O elements of a 15% LNMC622@ LRNMC composite. The characteristic peaks of Mn and O elements can be seen from FIGS. 5-a and b. However, the optical surface test was not sufficient, and therefore the particles were etched and XPS was measured every 2 nm. From fig. 5-d, we can see that the characteristic peaks of the O element in the surface layer and the inside are shifted continuously, and the deeper the depth, the larger the shift amount of the characteristic peaks. The change of the characteristic peak position of the O element is not obvious after about 10 nm. Similarly, the characteristic peak of Mn element in FIG. 5-c shows a similar change, but the characteristic peak of O element is more distinct.

This shows that the element distribution on the surface and inside of the microsphere prepared by the experiment is different, so that the method can be used as a basis for generating the 5% LNMC622@ LRNMC composite material. In addition, the XPS data also suggested that the resulting 5% LNMC622@ LRNMC composite was not a simple core-shell structure, but microspheres with a concentration gradient structure.

Example 6

The electrochemical performance of the LNMC622 material of example 2 and the 5% LNMC622@ LRNMC composite material of example 1 were tested by the following experiment and compared.

Half cells were assembled using a 2032 cell housing, assembled in a glove box with an argon atmosphere, and tested for relevant performance using the novyi cell test system. The working electrode composition of the cell was 5% LNMC622@ LRNMC: conductive carbon: PVDF is 8:1:1, and the electrode is loaded on an aluminum foil current collector.

Firstly, PVDF is weighed and prepared into 8 percent PVDF solution with anhydrous N-methyl pyrrolidone. Then, 5% of the material LNMC622@ LRNMC (80 wt.%), conductive carbon (10 wt.%), which was prepared in example 1, was weighed and placed in a reagent bottle, and stirred for 15min to uniformly mix the solid powder, and PVDF solution was added, wherein the effective mass of PVDF was (10 wt.%). Finally, a proper amount of NMP is dripped, the reagent bottle is sealed and then is placed on a stirrer to be stirred for 8-10h at 600 rpm. Coating the prepared slurry on an aluminum foil, and drying in a vacuum oven at 120 ℃ for more than 12 h.

And slicing the dried electrode slice, tabletting once on a roller, weighing the pressed electrode slice, recording the quality, and drying in a vacuum drying oven for 4-6 h. And finally, putting the dried electrode slice into a glove box for assembly. The counter and auxiliary electrodes of the cell were commercial lithium sheets. The electrolyte of the battery is high-voltage electrolyte LB-062, and the formula of the electrolyte is kept secret by a merchant. The comparative LNMC622 material and 5% LNMC622@ LRNMC are identical except for the active species. When testing the performance of a material at 1C, the material is typically activated for 2-3 cycles at 0.1C. The charging and discharging interval of the battery is 3.0-4.6V. In addition, the electrochemical impedance spectrum of the cell was tested by the electrochemical workstation using a two-electrode system. The electrochemical impedance spectrum is obtained under open-circuit potential, the amplitude is 5mV, and the frequency range is 0.01-10⁵Hz。

Fig. 6 shows the cycle performance of the LNMC622 and 5% LNMC622@ LRNMC materials prepared in examples 2 and 1 of the present invention at 1C, measured by the above experimental method. From the figure we can see that the 5% LNMC622@ LRNMC has significantly better cycling stability than the LNMC622 material. The discharge capacity of the first ring of the two is quite similar under 1C, and is about 150mAh/g, but in the subsequent circulation process, the decay speed of the LNMC622 is obviously faster than that of 5% LNMC622@ LRNMC.

Fig. 7 is a charge and discharge curve for LNMC622 and 5% LNMC622@ LRNMC composite 0.1C. The capacity of the 5% LNMC622@ LRNMC composite positive electrode material can still reach 130mAh/g after circulation for 200 times under 1C, the capacity retention rate is up to 84%, and compared with the original LNMC622 material, the capacity retention is improved by 24% in whole. This is a very obvious optimization, and can directly explain from the performance that the outer cladding of the LRNMC material is very useful for improving the performance of the LNMC 622.

Fig. 8 is a comparison of the rate performance of the two materials, from which we can easily see that the rate performance of the 5% LNMC622@ LRNMC composite material is better than that of the LNMC622 material, but the rate performance of the two materials is not very different. This is because the conductivity of the coating layer LRNMC itself is not better than that of the LNMC622 material, so the conductivity of the 5% LNMC622@ LRNMC is not greatly improved, and the performance improvement space of the material under high rate is not large. However, the rate performance of the 5% LNMC622@ LRNMC is still improved compared with the LNMC622 material in general, which may be that the preparation process of the 5% LNMC622@ LRNMC has one more sintering process, so that the crystallinity of the material is better.

Fig. 9 shows the impedance test for two materials activated at 0.1C for 3 cycles, and the LNMC622 impedance is slightly less than the 5% LNMC622@ LRNMC material, but the difference is not very large, but after 200 cycles at 1C, we can clearly see that the LNMC622 impedance is greater than 5% LNMC622@ LRNMC. This means that the LNMC622 after cycling produces a phase change layer and the area of this phase change layer is very large, which then results in the LNMC622 after cycling having a much higher resistance than after activation. In addition to the phase change layer causing the resistance of the material to become large, the electrolyte in the battery may undergo a certain side reaction during the circulation process, which may be the electrochemical reaction of the electrolyte itself under the voltage window or the mutual reaction of the electrolyte contacting the surface of the material. These side reactions also result in a large impedance of the cell.

FIG. 10 shows the electrochemical performance of examples 2-5 according to the same test method as described above, and the data is compared in the following table, and the performance of example 1 is shown for comparison.

Examples 2 to 5: examination of raw material dosage ratio

Examples	1	3	4	5	6
						Discharge capacity (mAh/g)	139.06	102.93	118.91	100.03	103.39
Capacity retention (%)	88.2％	71.1	79.1	73.1	73.4

After comparison of the examples, it is found that when the coating amount of 5% of LNMC622@ LRNMC circulates for 100 cycles under 1C, the discharge capacity can still reach 139mAh/g, the capacity retention rate is as high as 88.2%, the pure LNMC622 is only 102.93mAh/g, 71.1%, and the discharge capacity and the capacity retention rate of other coating amounts of LNMC622@ LRNMC are further improved compared with the pure LNMC622, and specific data are shown in the table.

Various corresponding changes and modifications can be made by those skilled in the art based on the above technical solutions and concepts, and all such changes and modifications should be included in the protection scope of the present invention.

Claims

1. A preparation method of an LNMC622@ LRNMC composite material comprises the following steps:

s1: preparation of LRNMC microparticles:

s1.1: adding zirconium oxide ball milling beads with the diameter of 0.1-0.6 mm and an LRNMC material into an anhydrous n-hexane solution for ball milling, wherein the ball milling speed is set to be 300-600 rpm, and the time is 20-60 hours;

s2: preparation of LNMC622 material:

S3: preparation of LNMC622@ LRNMC composite material

S3.3: and (4) putting the mixed material obtained in the step (S3.2) into a vacuum drying oven, drying for 1-4 h at 40-80 ℃, putting the dried material into a porcelain boat, and putting the porcelain boat into a tube furnace for calcination. The calcination conditions were: introducing high-purity oxygen, heating at a rate of 2-10 ℃/min, and heating to 600-900 ℃ to calcine for 1-4 h. And cooling to obtain the LNMC622@ LRNMC composite material.

In step S1, the LRNMC is Li_1.2Ni_0.13Mn_0.54Co_0.13O₂；

In step S2, the LNMC622 is Ni_0.6Mn_0.2Co_0.2(OH)₂。

2. The method for preparing an LNMC622@ LRNMC composite material as claimed in claim 1, wherein in step S1.1, 15-35 g of zirconia balls with a diameter of 0.1 mm-0.6 mm are weighed, and 1-5 g of LRNMC is weighed and added into 3-8 mL of anhydrous n-hexane; step S2.1, specifically, weighing a certain amount of NMC622 precursor, and then weighing anhydrous LiOH with the amount of 0.5-1.5 times of that of LNMC 622; step S3.1 specifically includes adding 0.1-0.5 g of LRNMC material into a reagent bottle, and adding 3-8 mL of anhydrous n-hexane as a dispersing agent; step S3.2 is to add 1-3 g of lnmc622 material to the dispersion liquid obtained in step S3.1 after the ultrasonic treatment.

3. LNMC622@ LRNMC composite material obtained by the preparation method according to claims 1-2.

4. Use of the LNMC622@ LRNMC composite material obtained by the preparation method according to claims 1 to 4 in a battery.